When the expansion is complete, Dart will also transfer Solo Cup’s corporate and administrative operations from Lake Forest to Mason.

The new headquarters will be Dart’s largest office building and can house about 400 employees. The expansion will create 325 jobs, some of which will be filled by transferred Solo Cup employees.

Dart will break ground on the project in 2013 and it should be completed by 2014. Solo’s Lake Forest office will remain open through 2013, but Dart hasn’t made any final decisions on the future of the building or how many employees will be transferred, she said.

“We’re in the midst of integrating the two companies. Our focus is on a successful integration,” she added.

The company received a $3 million performance-based grant from the Michigan Business Development Program for the expansion.

“We’re really excited that the growth of the company will create hundreds of new jobs in Michigan,” Barrage said. “It’s just further evidence of Dart’s long commitment to our state.”

Dart is one of the largest manufacturers of plastic and paper single-use foodservice packaging. With the Solo Cup acquisition, the company has about 15,000 employees and more than 45 plants, distribution centers and office locations worldwide.

Dart has estimated thermoforming sales of $1.27 billion and estimated total sales of more than $3 billion.